1. Field of the Invention
The present invention relates to testing systems, and more particularly, to a driver circuit for use in testing bidirectional semiconductor devices.
2. Description of the Related Art
Testing systems for semiconductor logic and array products must meet ever increasing demands as product circuit complexities, operating speeds and pin count requirements continue to burgeon. Faster product operating speeds correspondingly require that the testers operate at higher data rates. Greater product circuit complexity calls for increased test pattern generator flexibility and sophistication. Product pin availability restrictions create the need for increased functionality of a pin to operate as an input and/or output, which requires that the testers be adapted to access product circuits (i.e., to apply test signals and to extract circuit responses thereto) without sacrificing performance.
One known technique to limit the number of pins on high density product circuits involves the use of common input-output (I/O) circuit terminal pins, to permit bi-directional communication at different times. When testing such products, test signals are applied and the circuit response thereto is received at mutually exclusive times using the same pin. Other products extend the common I/O technique by enabling the simultaneous bidirectional communication of data between chips over the same interchip cable path using a single circuit accessing pin on each chip. One example of such a simultaneous bi-directional transceiver circuit is described in U.S. Pat. No. 4,690,800, issued on Oct. 6, 1987 to Joseph R. Cavaliere et al, and assigned to the present assignee.
As explained in the cited patent, each transceiver circuit receives an input bilevel data signal and a trilevel signal from one end of the interchip cable and produces an output bilevel data signal therefrom representing the data (if any) being transmitted simultaneously from a second transceiver circuit connected to the opposite end of the interchip cable. Thus, in order to test ordinary bidirectional receivers (common I/O), bilevel test signals are required from the tester whereas trilevel test signals are needed from the tester to test simultaneous bi-directional transceivers (Si-Bi-Di).
It should be noted that each nominal level of the bilevel or trilevel test signals must be individually adjustable during the test to assure that the product voltage level response is within acceptable tolerance limits. Moreover, voltage level changes must be produced by the tester after extremely short intervals so that overall testing time is kept to an acceptable minimum, and the product being tested is characterized at its maximum cycle time regardless of how the pin is configured.